.alpha.-Polyglutamic acid has been used as materials of artificial leather and the like, while .gamma.-polyglutamic acid has been known as a component of viscous materials of a Japanese fermented soybean food called natto. In recent years, attempts have been made to produce .gamma.-polyglutamic acid as a new material by means of a large scale culturing. The present inventors have developed a process for the economical production of .gamma.-polyglutamic acid in a large scale using a bacterium belonging to the genus Bacillus (JP-A-1-174397; the term "JP-A" as used herein means an "unexamined published Japanese patent application").
The .gamma.-polyglutamic acid produced by culturing a bacterium belonging to the genus Bacillus has a molecular weight of more than 1,000,000. It is useful as a viscosity-adding agent but not applicable to other use because of its too high viscosity. Polyglutamate hydrolase produced by Micromonospora melanosporea IFO 12515 (T. Muro et al., Agr. Biol. Chem., 54(4), 1065, (1990)) and .gamma.-glutamyl transpeptidase are known as enzymes which reduces molecular weight of .gamma.-polyglutamic acid. The substrate of the former enzyme is .alpha.-polyglutamic acid and that of the latter is .gamma.-polyglutamic acid. Both enzymes act as exo-acting enzymes by cleaving and liberating glutamic acid consecutively from the end of the polyglutamic acid chain. To date, no endo-acting enzyme which hydrolyzes .gamma.-polyglutamic acid has been known. Thus, it has been desired to develop an enzyme which can reduce molecular weight of .gamma.-polyglutamic acid by hydrolyzing it with an endo action.
It is reported that .gamma.-polyglutamic acid produced by fermentation is considered a mixture of a homopeptide composed of L-glutamic acid, namely poly-L-glutamic acid, and a homopeptide composed of D-glutamic acid, namely poly-D-glutamic acid (S. Murao, Kohbunshi, 16(188), 1204-1212 (1969)).